An electromagnetic launcher based on induction coilgun technology comprises coil electromagnets. The coils are sequentially arranged along a launch tube to accelerate a projectile to a desired velocity for launch. The coils are powered on and off in sequence to accelerate the projectile and expel it out of the launch tube. The sequentially-arranged coils and their accompanying circuits are commonly known as the “stages” of the coilgun. See FIG. 1.
The coilgun acts as a linear induction motor with respect to the projectile. The projectile is associated with an armature circuit that is part of, or coupled with, or supports the projectile. When powered, the propulsion coil inductively couples to an armature coil in the armature circuit as it passes the propulsion coil. A coilgun provides no physical contact between the projectile and the propulsion coil. The acceleration is achieved through induction and magnetic forces. In contrast, a railgun uses sliding contacts or rails to transmit energy to the projectile.
Coilguns are often designed by and for hobbyists for low-power applications that shoot light payloads. However, larger systems have been disclosed for defense applications. For example, U.S. Pat. No. 7,549,365 B2 discloses an electromagnetic missile launcher (“EMML”) with a catapult-sled that supports a missile as it is being launched. The catapult-sled is electromagnetically accelerated by induction as between armature coils on the catapult-sled and successively arranged propulsion coils along the launch tube. The EMML launcher has multiple cells, each cell being equipped with the coilgun and catapult-sled. The armature is part of the sled that guides, but does not launch with, the projectile. U.S. Pat. No. 7,549,365 B2 is hereby incorporated by reference herein. If there are any contradictions or inconsistencies between the present case and one or more of the cases that are incorporated by reference herein, the claims in the present case are to be interpreted consistent with the language herein.
Another catapult-style electromagnetic launcher is the “Electro Magnetic Countermeasure Launcher” (“EMCL”) in U.S. Pat. No. 7,895,931, which is incorporated by reference herein. The illustrative EMCL has a coilgun-based design that uses an electromagnetic catapult to throw a countermeasure device with controlled force and direction, while minimizing the launch signature. The EMCL comprises a launch tube that propels a series of countermeasure payloads. The EMCL typically requires repetitive firings from the same set of propulsion coils in relatively rapid succession (i.e., burst), because the same launch tube is used to launch the series of countermeasure payloads. The equipped armatures are ejected with or as a part of the countermeasure payload. Additional payloads are loaded and then fired from the same launch tube.
One drawback of coilgun-based designs arises from the residual energy that is left over in the propulsion coil(s) and associated propulsion circuitry after firing. The residual energy dissipates as heat in the propulsion coil. See FIG. 2B. The coilgun operator must then wait for the coil to cool down before the coilgun is ready to fire/launch again. Additionally, the excess heat tends to lower the longevity of the coil. In a weapons-grade coilgun, the propulsion coil is an expensive component, and replacing the coil takes a substantial toll on the weapon's maintainability. Moreover, the excess heat makes the weapon vulnerable to infrared detection. FIGS. 1, 2A, and 2B illustrate some of the abovementioned principles of the prior art.
FIG. 1 depicts the salient elements of a typical induction coilgun system in the prior art, including coilgun 100 and projectile 107. Coilgun 100 comprises: propulsion circuits 101-1, 101-2, and 101-3; and launch tube 105; each propulsion circuit 101-j comprises propulsion coil 103-j and power supply 111-j, where j=1, 2, 3. Coilgun 100 is illustrated with three stages, 1, 2, and 3, each stage comprising only one propulsion circuit 101-j, but it will be clear to those having ordinary skill in the art that any number of stages and any number of component propulsion circuits per stage are possible.
Propulsion coil 103-j is well known in the art; when electrical current flows through it, the propulsion coil is capable of inductively coupling to an armature coil that falls within its inductive influence as it travels through the launch tube.
Launch tube 105 is well known in the art and encloses, supports, and/or guides accelerating projectile 107.
Projectile 107 is accelerated by the launcher to travel in the direction of the arrow as shown. The illustrative projectile 107 comprises armature circuit 109 that, through inductive coupling to the successively arranged propulsion coils 103-j in the corresponding propulsion circuits 101-j, enables projectile 107 to accelerate out of launch tube 105.
Power supply 111-j is well known in the art and acts as a power source to propulsion circuit 101-j. 
Control sub-systems are not shown in the present figure or in FIGS. 2A and 2B. Electronics (accompanied by hardware and/or software) may be used as the control sub-system in some embodiments of coilgun 100 to operate the coilgun. In some embodiments, the control sub-system is manual.
FIG. 2A depicts the salient elements of prior art propulsion circuit 101-j while in the firing state; also shown is armature circuit 109, which is associated with projectile 107 (not shown), and which comprises armature coil 209. Propulsion circuit 101-j comprises the following salient electrical components: propulsion coil 103-j; capacitor 201; switch 203; and diode 205. Each of these electrical components is well-known in the art. During the firing state, switch 203 is in a closed position and electrical current 207 flows through a loop that comprises capacitor 201, switch 203, and propulsion coil 103-j. In the firing state, propulsion coil 103-j inductively couples to armature coil 209 as projectile 107 (not shown) accelerates through launch tube 105 (not shown).
FIG. 2B depicts the salient elements of prior art propulsion circuit 101-j while in the post-firing state. The post-firing state follows the firing state of FIG. 2A. Propulsion circuit 101-j comprises the same salient electrical components as shown in FIG. 2A. During the post-firing state, switch 203 is in an open position and electrical current 211 flows through a loop that comprises diode 205 and propulsion coil 103-j. 
In the post-firing state, propulsion coil 103-j experiences a rise in temperature that arises from residual energy left over from the firing state. As electrical current 211 flows, it heats propulsion coil 103-j through resistive dissipation of the coil windings, manifesting as heat 213. As noted, the temperature rise and the heat dissipation are significant drawbacks.